The present invention relates to a system for controlling fuel injection by means of an electromagnetic valve.
A fuel injection system of electromagnetic-valve controlled type for use in diesel engines is disclosed, for example, in Japanese Patent Appln. Laid-Open Nos. 56-151228, 56-154134, 61-268844, 61-286541 and 61-286716, U.S. Pat. No. 4,395,987 corresponding to the above Japanese Patent Appln. Laid-Open Nos. 56-151228 and 56-154134, and U.S. Ser. No. 865,125 filed on May 8, 1986 corresponding to the above Japanese Patent Appln. Laid-Open No. 61-268844. The fuel injection system of this kind comprises a fuel injection pump as a basic component. The fuel injection pump includes a pump housing, a plunger associated with the pump housing for reciprocative movement in interlocked relation to a crankshaft of the engine, and a fuel pressurizing chamber associated with the pump housing and having a volume variable in response to reciprocative movement of the plunger. The fuel pressurizing chamber communicates with a fuel supply source through a supply passage, and communicates with fuel injection nozzles of the engine through forcible delivery passage means. The supply passage is closed during a major portion of a forward stroke of the plunger, and is opened during a backward stroke of the plunger. In addition, a release passage is provided, which is connected to the fuel pressurizing chamber and which is adapted to be opened and closed by an electromagnetic valve. During the forward stroke of the plunger which reduces the volume of the pressurizing chamber, the fuel is released from the fuel pressurizing chamber through the release passage for a period within which the electromagnetic valve is in an open position. On the other hand, the fuel is forcibly delivered to the fuel injection nozzles of the engine through the forcible-delivery passage means only for a period within which the electromagnetic valve is in a closed position.
The above-described electromagnetic valve is usually controlled in the following manner. That is, rotation detecting means outputs reference pulses each indicative of passage of the engine crankshaft through a reference rotational position, and scale pulses indicative of angular movement of the crankshaft every a predetermined angular extent. In response to receipt of the reference pulses and the scale pulses from the rotation detecting means, control means calculates current rotational angle of the crankshaft and current number of revolutions per unit time or rotational speed thereof. The control means also receives data from a sensor for detecting an amount of depression of an accelerator pedal and a sensor for detecting temperature of engine cooling water. On the basis of these data and the engine rotational speed calculated as described above, the control means calculates a target injection timing and a target fuel injection amount. On the basis of the results of this calculation, the control means outputs a drive pulse for a closing command to a drive circuit for the electromagnetic valve. The drive pulse has a time duration corresponding to the target fuel injection amount. The drive pulse is outputted when the current rotational angle of the engine crankshaft reaches a target injection timing.
By the way, in the system disclosed in the above patents, a starter motor is operated at start-up of the engine to rotate the crankshaft. The plunger is reciprocated in interlocked relation to the crankshaft. In this connection, the control means cannot calculate the rotational angle of the crankshaft, until the control means receives the first reference pulse from the rotation detecting means, indicative of passage of the crankshaft through the reference rotational position. By this reason, the control means does not output the drive pulse for the closing command to the drive circuit for the electromagnetic valve. Thus, during the forcible-delivery stroke of the plunger, the fuel within the fuel pressurizing chamber is released through the release passage means, so that the fuel is not injected. Accordingly, at the initial stage of the start-up, torque due to combustion of fuel is not entirely generated, but torque is generated only by the starter motor. Thus, such a problem might arise that the start-up is not stabilized.
In a fuel injection system disclosed in Japanese Patent Application Laid-Open No. 61-258951, the electromagnetic valve is maintained closed until the reference pulses each indicative of passage of the crankshaft through the reference rotational position is outputted, and fuel is injected over the entire period of the forward stroke of the plunger. Since, in this system, fuel injection is carried out from the beginning at the engine start-up, the start-up is stabilized. However, the system has such a problem that, because the fuel is supplied excessively, black smoke is produced from the engine.
Japanese Patent Application Laid-Open No. 61-8440 discloses a system in which when a microcomputer is temporarily brought to a malfunction state at the start-up, a drive pulse of a given duty ratio is outputted to an actuator, and a control rack of the fuel injection pump is controlled by the actuator so as to be brought to a predetermined position, thereby controlling the fuel injection amount to a predetermined value. However, the system is not of electromagnetic-valve controlled type, and is not believed relevant to the present invention.